An active matrix type liquid crystal display device such as a liquid crystal display uses a thin film transistor (hereinafter referred to as the TFT) as a switching element and includes a transparent pixel electrode, an interconnection portion such as a gate interconnection, a source/drain interconnection, etc., the TFT substrate having a semiconductor layer of amorphous silicon (a-Si), polycrystal silicon (p-Si), etc., a counter substrate having a common electrode opposed to the TFT substrate at a predetermined distance, and a liquid crystal layer filled between the TFT substrate and the counter substrate.
In the TFT substrate, pure Al and an Al alloy such as Al—Nd (hereinafter referred to collectively as Al type alloy) are generally used for the interconnection material such as a gate interconnection and a source/drain interconnection with a reason that the specific resistivity is low, fabrication is easy, etc. A barrier metal layer comprising a high melting metal such as Mo, Cr, Ti, and W is usually disposed between the Al type alloy interconnection (Al type alloy film) and the TFT semiconductor layer of a TFT as typically represented by a patent document 1, etc. This is attributable to that when the Al type alloy interconnection is in direct contact with the TFT semiconductor layer of the TFT without interposition of the barrier metal layer, Al in the Al type alloy interconnection diffuses into the semiconductor layer to deteriorate TFT property by thermal hysteresis in the subsequent steps (for example, a deposition step for an insulative layer formed above the TFT or a thermal step such as sintering and annealing). Specifically, a current flowing through the TFT (off current during switching-OFF time and on current during switching-ON time), etc. undergoes an undesired effect to increase the off current and decrease the on current and, in addition, also lower the switching speed (switching-on responsivity to electric signals). Further, also the contact resistance between the Al type alloy interconnection and the semiconductor layer may sometimes also increase.
As described above, while the barrier metal layer is effective for suppressing interdiffusion between Al and Si at the boundary between the Al type alloy film and the semiconductor layer, a deposition apparatus for forming a barrier metal is additionally required in order to form the barrier metal layer in addition to the deposition apparatus for forming the Al type alloy interconnection. Specifically, extra-deposition apparatus provided with deposition chambers respectively for forming barrier metals additionally (typically, a cluster tool where a plurality of deposition chambers are connected to a transfer chamber) have to be used which increases the manufacturing cost and lowers the productivity. Further, since the fabrication speed is different between the metal used as the barrier metal layer and the Al type alloy of the fabrication steps such as wet etching using liquid chemicals, it is extremely difficult to control the fabrication size in the lateral direction in the fabrication step. Accordingly, formation of the barrier layer complicates the steps, increases the manufacturing cost and lowers the productivity not only with a view point of deposition but also with a view point of fabrication.
While descriptions have been made to an example of a liquid crystal display device as a typical example of a display device, the problem attributable to the interdiffusion between Al and Si at the boundary between the Al type alloy film and the semiconductor layer described above is observed not only in the display device but also in the semiconductor device such as LSI, FET, etc. For example, in the manufacture of LSI as a typical example of the semiconductor device, an Al type alloy film is deposited after forming a barrier metal layer such as of Cr or Mo on the semiconductor layer in order to prevent occurrence of spikes formed at the boundary between the semiconductor layer and the Al type alloy film, simplification of the steps and decrease of the cost are demanded also in the field of the semiconductor device.
Accordingly, it has been demanded for providing a technique capable of avoiding the problem due to interdiffusion between Al and Si caused in the display device or the semiconductor device without providing the barrier metal layer as in the usual case.
In view of the situations described above, patent documents 2 to 4, for example, propose a direct contact technique capable of saving the formation of the barrier metal layer and capable of direct contact of the Al type alloy interconnection used for the source/drain electrode, etc. with the semiconductor layer. Among them, the patent document 4 is disclosed by the present applicant and discloses an interconnection structure having a material comprising a nitrogen-containing layer and an Al type alloy film in which N (nitrogen) of the nitrogen-containing layer is bonded with Si in the semiconductor layer. It is considered that the nitrogen-containing layer acts as a barrier layer for preventing interdiffusion between Al and Si and it demonstrates that excellent the TFT property can be obtained without forming a barrier metal layer such as of Mo as in the existent technique. Further, since the nitrogen-containing layer can be manufactured simply and conveniently by a nitridation treatment such as plasma nitridation after forming the semiconductor layer and before depositing the Al type alloy film, it has a merit that no extra-deposition apparatus for forming the barrier film is necessary.
[Prior Art Document]
[Patent Document]
[Patent Document 1] JP-A No. 2000-199912
[Patent Document 2] JP-A No. 2003-273109
[Patent Document 3] JP-A No. 2008-3319
[Patent Document 4] JP-A No. 2008-10801